This invention relates to a method of manufacturing electronic parts, based on the transferred bump process.
Recent efforts aimed at miniaturizing a semiconductor chip used in, for example, an IC, LSI, etc., have been accompanied by efforts to reduce the size of its package. The package has a role of an electrode lead to extend from an aluminium electrode on the semiconductor chip, thereby to allow for its easy handling and to protect it from external pressure. The extending of a lead from the aluminium electrode of the semiconductor chip to the terminal of the package can be conveniently effected by use of the tape automated bonding (TAB) process.
The TAB process consists in forming a bump on the electrode and effecting connection between the bump and the electrode lead. It is necessary to use electroplating in order to mount an Au bump on the Al electrode of the semiconductor substrate. However, since it is difficult to directly adhere an Au bump to an Al electrode, the customary process is to deposit a multiple barrier metal mass composed of, for example, Cu, Cr and Ti on the Al electrode, before performing plating.
As a result, a bump-transferring process has been devised which comprises the steps of first forming a bump on a substrate, transferring the bump to a lead, and then to the desired electrode, and thermally pressing the bump to effect the connection with the electrode (Japanese Patent Disclosure Nos. 57-152147 and 60-92648). This proposed process dispenses with the aforementioned barrier metal, thereby simplifying the formation of the bump and the bump assembly, and enabling a plurality of electrodes to be simultaneously connected to terminals.
FIGS. 1A to 1E show the sequential steps of the bump-transferring process. As is shown in FIG. 1A, substrate 5 on which a bump is to be formed is constructed by laminating conductive layer 2, conductive oxide layer 3, and resist pattern 4, in that order, on base-substrate 1. Bump 6 is electroplated in the bump-forming opening of substrate 5. Conductive oxide layer 3 should preferably be prepared from a material which can be readily connected to gold bump 6 and easily released from bump 6 when it is transferred to the lead. In the second step, (FIG. 1B), electrode lead member 8, supported on insulating film 7, is placed on bump 6. Thereafter, heated bonding tool 9 is pressed on electrode lead member 8, thereby transferring bump 6 to electrode lead 8 (FIG. 1C). Later, as can be seen in FIG. 1D, bump 6 transferred to electrode lead 8 is positioned above al electrode (bonding pad) 12 exposed out of passivation layer 11 of semiconductor chip 10. Thereafter, previously heated bonding tool 9 is pressed on electrode lead 8, thereby connecting electrode lead 8 to Al electrode 12, with bump 6 interposed therebetween.
However, the above-mentioned bump-transferring process has drawbacks in that the bump tends to peel off from an oxide layer, to which it is adhered, during the step of electroplating the bump on the substrate and also during the subsequent bump-washing step, thus resulting in a decline in throughput.